[Javascript] Genetic Algorithm String Matcher by bkanber

[tom_mai78101]

I modified one line of code in the original code by bkanber, to absolutely ensure the result with the best fitness will always be inherited by its children.

Modified code is given as follows:

var Gene = function(code) {
    if (code) this.code = code;
    this.cost = 9999;
};
Gene.prototype.code = '';
Gene.prototype.random = function(length) {
    while (length--) {
        this.code += String.fromCharCode(Math.floor(Math.random() * 255));
    }
};
Gene.prototype.mutate = function(chance) {
    if (Math.random() > chance) return;

    var index = Math.floor(Math.random() * this.code.length);
    var upOrDown = Math.random() <= 0.5 ? -1 : 1;
    var newChar = String.fromCharCode(this.code.charCodeAt(index) + upOrDown);
    var newString = '';
    for (i = 0; i < this.code.length; i++) {
        if (i == index) newString += newChar;
        else newString += this.code[i];
    }

    this.code = newString;

};
Gene.prototype.mate = function(gene) {
    var pivot = Math.round(this.code.length / 2) - 1;

    var child1 = this.code.substr(0, pivot) + gene.code.substr(pivot);
    var child2 = gene.code.substr(0, pivot) + this.code.substr(pivot);

    return [new Gene(child1), new Gene(child2)];
};
Gene.prototype.calcCost = function(compareTo) {
    var total = 0;
    for (i = 0; i < this.code.length; i++) {
        total += (this.code.charCodeAt(i) - compareTo.charCodeAt(i)) * (this.code.charCodeAt(i) - compareTo.charCodeAt(i));
    }
    this.cost = total;
};
var Population = function(goal, size) {
    this.members = [];
    this.goal = goal;
    this.generationNumber = 0;
    while (size--) {
        var gene = new Gene();
        gene.random(this.goal.length);
        this.members.push(gene);
    }
};
Population.prototype.display = function() {
    document.body.innerHTML = '';
    document.body.innerHTML += ("<h2>Generation: " + this.generationNumber + "</h2>");
    document.body.innerHTML += ("<ul>");
    for (var i = 0; i < this.members.length; i++) {
        document.body.innerHTML += ("<li>" + this.members[i].code + " (" + this.members[i].cost + ")");
    }
    document.body.innerHTML += ("</ul>");
};
Population.prototype.sort = function() {
    this.members.sort(function(a, b) {
        return a.cost - b.cost;
    });
}
Population.prototype.generation = function() {
    for (var i = 0; i < this.members.length; i++) {
        this.members[i].calcCost(this.goal);

    }

    this.sort();
    this.display();
    var children = this.members[0].mate(this.members[1]);
    this.members.splice(this.members.length - 2, 2, children[0], children[1]);

    for (var i = 1; i < this.members.length; i++) { //Modified line. Was "var i = 0; "
        this.members[i].mutate(0.5);
        this.members[i].calcCost(this.goal);
        if (this.members[i].code == this.goal) {
            this.sort();
            this.display();
            return true;
        }
    }
    this.generationNumber++;
    var scope = this;
    setTimeout(function() {
        scope.generation();
    }, 20);
};


var population = new Population("Hello, world!", 21);
population.generation();

Original source (JSFiddle)